The present invention relates to a vacuum turbopump with bearing assembly and more particularly to the vacuum turbopump with a magnetic bearing system with backup bearings and sensors contained within or inside the shaft of the turbomolecular vacuum pump.
A suitable vacuum pump for which the present invention may be utilized is described in the U.S. Pat. No. 5,238,362 assigned to Varian Associates that is incorporated by reference herein. The vacuum pump described in '362 patent is a turbomolecular vacuum pump having an increased compression ratio which is capable of extending the operating range towards higher pressures. Turbomolecular pumps of this type can utilize magnetic bearings and actively control five degrees of freedom of the rotating pump member. A magnetic bearing system with backup supports inside the shaft has been disclosed in the U.S. patent application Ser. No. 08/858,230 "A Rotatable Assembly for Supporting of the Rotor of a Vacuum pump", which is assigned to Varian Associates, Inc. and the description of the bearing assembly for supporting the rotor of the vacuum pump with hollow shaft is hereby incorporated by the reference.
FIG. 1, FIG. 2 and FIG. 3 show schematically a conventional magnetic support for a rotor of the vacuum pump with different shape of the suspended parts. Reference numeral 10 designates a pumping rotor, 20 is a backup bearing, 30 is a magnetic radial bearing stator, 40 is a stator of an electric motor, 50 is a magnetic axial bearing stator and 60 is a shaft. The rotor shown in FIG. 1 has a cantilever structure, while the rotor shown in FIG. 2 and FIG. 3 have a bell-shaped rotor pumping portion. The bell-shaped rotor allows for location of the rotor's center of gravity between the radial magnetic bearings. This bell-shaped rotor is often used in medium or large size turbomolecular pumps horizontally mounted to reduce or eliminate the radial loads on bearings due to tilting moment.
The magnetically suspended pump disclosed in the U.S. Pat. No. 4,023,920 "Turbomolecular as a Vacuum Pump having a Magnetic-Bearing Supported Rotor", belongs to the type of magnetic support for a pump rotor shown in FIG. 3, wherein the magnetic bearing stators, electric motor stator and backup bearings are positioned inside the bell-shaped rotor. The magnetic bearing rotors and electric motor rotor are located in the bell bore for eliminating the connection between the shaft and the bell-shaped rotor. This design being advantageous in certain respects increases the size of the pump since the magnetic and backup bearings are placed in series along the axis of the rotor shaft.
Therefore, it would be desirable to provide an improved bearing assembly which could be utilized in turbomolecular vacuum pumps with increased compression ratios which provide radial and axial sensing while providing for a smaller system length.